add containsTopic method

channel/channel-server/src/main/java/com/alibaba/arthas/channel/server/message/MessageExchangeService.java

@@ -31,6 +31,13 @@ public interface MessageExchangeService {
 
     void subscribe(Topic topic, int timeout, MessageHandler messageHandler) throws MessageExchangeException;
 
+    /**
+     * Whether exists the specify topic
+     * @param topic
+     * @return
+     */
+    boolean containsTopic(Topic topic);
+
     interface MessageHandler {
         /**
          * handle message

channel/channel-server/src/main/java/com/alibaba/arthas/channel/server/message/impl/MessageExchangeServiceImpl.java

@@ -101,6 +101,11 @@ public class MessageExchangeServiceImpl implements MessageExchangeService {
         }
     }
 
+    @Override
+    public boolean containsTopic(Topic topic) {
+        return topicMap.containsKey(topic);
+    }
+
     @Override
     public void pushMessage(Topic topic, byte[] messageBytes) throws MessageExchangeException {
         TopicData topicData = topicMap.get(topic);

channel/channel-server/src/main/java/com/alibaba/arthas/channel/server/redis/RedisMessageExchangeServiceImpl.java

@@ -79,6 +79,11 @@ public class RedisMessageExchangeServiceImpl implements MessageExchangeService {
         }
     }
 
+    @Override
+    public boolean containsTopic(Topic topic) {
+        return redisTemplate.hasKey(topic.getTopic()).block();
+    }
+
     @Override
     public void pushMessage(Topic topic, byte[] messageBytes) throws MessageExchangeException {
         String key = topic.getTopic();